77. THE VIRAL REPLICATIVE CYCLE

Question 1

1. What are viruses?

Answer 1

• they are obligate, intracellular parasites

OBLIGATE:
- the virus cannot survive without oxygen

Question 2

2. Where do viruses replicate?

Answer 2

• they replicate within the host cell

Question 3

3. What are the 3 main stages of the Viral Replicative Cycle?

Answer 3

1. Attachment and Entry to the Host Cell
2. Virus Replication
3. Assembly and Release

Question 4

4. Define what happens during the:
   Attachment and Entry to the Host Cell.

Answer 4

• the viral particles and the viral genome enter the
  host cell

Question 5

5. Define what happens during the:
   Virus Replication.

Answer 5

• the virus will use the host’s replication organelles
• it will replicate the viral genome
• it will produce the viral proteins

Question 6

6. What are some examples of Replication Organelles?

Answer 6

• enzymes
• ribosomes
• tRNAs
• amino acids
• ATP

Question 7

7. Define what happens during the:
   Assembly and Release.

Answer 7

• the Viral Nucleic Acid molecules and the Capsomeres
  will self-assemble
• they will join with one another spontaneously
• they will form a new virus
• this is released from the cell

Question 8

8. What are the 8 Specific Stages of the Viral Replicative Cycle?

Answer 8

1. Attachment
2. Penetration
   - the entry of the Virus into the host cell
3. Un-coating of the Viral Genome
   - the capsomere will fall apart
4. Replication
5. Gene Expression
6. Assembly
7. Release
   - this is the exit of the virus from the cell
8. Maturation
   - this only happens for enveloped viruses

Question 9

9. What causes variations in the Viral Replicative Cycles?

Answer 9

• the type of Nucleic Acid
• the presence of a viral envelope
• this affects the penetration of the virus into the cell
• it affects the release of the virus from the cell

Question 10

10. What happens during: Attachment?

Answer 10

• the virus is attached to the host cell

Question 11

11. What happens in Enveloped Viruses during: Attachment?

Answer 11

• the glycoproteins on the viral envelope will attach to
  the receptors of the host cell
• these receptors are found on the plasma membrane of
  the host cell

Question 12

12. What happens in Non-Enveloped Viruses during: Attachment?

Answer 12

• the fibres (spikes) on the viral capsid
• will attach to the receptors of the host cell
• these receptors are found on the plasma membrane of
  the host cell

Question 13

13. What happens during: Penetration?

Answer 13

• this is the entry of the virus into the host cell

Question 14

14. What happens in the Enveloped Viruses during:
    Penetration?

Answer 14

• the enveloped viruses will enter the host cell
• this happens by membrane fusion

MEMBRANE FUSION:
- the viral envelope will fuse with the plasma membrane
of the host cell
- this releases the capsid into the host cell

Question 15

15. What happens in the Non-Enveloped Viruses during:
    Penetration?

Answer 15

• the enveloped viruses will enter the host cell
• this happens by Endocytosis

MEMBRANE FUSION:
- the virus is enclosed in a vesicle
- it sits on the membrane of the host cell
- it is ingested into the cell

Question 16

16. What happens during:
    the Uncoating of the Viral Genome?

Answer 16

• the capsomeres will fall apart
• this will affect the Capsid
• this releases the contents of the virus into the cell

THE CAPSOMERES:
- are catalysed by Lysosomal Enzymes

Question 17

17. What happens during:
    Virus Replication in the Host Cell?

Answer 17

• the viral genome will be replicated in the host cell
• new viral proteins will be produced in the host cell

THERE WILL BE DIFFERENT REPLICATION MECHANISMS:
- these are based on the viral genome type
- there are 4 types of viruses based on their nucleic
acid

Question 18

18. What are the four types of Viruses based on their Nucleic Acid?

Answer 18

1. Double Stranded DNA Viruses (ds DNA)
2. Single Stranded DNA Viruses (ss DNA)
3. Double Stranded RNA Viruses (ds RNA)
4. Single Stranded RNA Viruses (ss RNA)

Question 19

19. What happens during: Viral Assembly?

Answer 19

• the Capsomeres will assemble
• the Capsomeres are the proteins of the Virus
• they will form new capsids when they assemble

THE CAPSIDS:
- will encapsulate the new viral genomes
- this produces new viral particles

Question 20

20. What happens during: the Viral Release?

Answer 20

• this is the exit of the virus from the cell

Question 21

21. What happens in Enveloped Viruses during:
    Viral Release?

Answer 21

• the virus is released from the host cell
• this happens through Budding
• the host cell is destoyed

BUDDING:
- this is when the virus acquires an envelope
- the virus undergoes maturation

Question 22

22. How is the Host Cell destroyed during Viral Release in Enveloped Viruses?

Answer 22

• the permeability of the plasma membrane changes
• this is because of the presence of the Viral Proteins
• the gene expression of the host cell is inhibited
• the virus steals the enzymes from the host cell
• the host cell cannot produce proteins
• it dies

Question 23

23. What happens in Non-Enveloped Viruses during:
    Viral Release?

Answer 23

• the virus is released from the host cell
• this happens through Lysis

LYSIS:
- this happens to the host cell
- its plasma membrane is destructed
- this happens due to the Lysosomal Enzymes